Here is a quick simple program to get you started with reading and writing data from the serial port using Visual Basic .Net 2005.

Imports System
Imports System.IO.Ports
Imports System.Threading

Public Class Module1
 Shared ser As SerialPort
 Shared cont As Boolean

 Public Shared Sub Main()
  Dim message As String
  ser = New SerialPort()
  Dim readThread As Thread = New Thread(AddressOf Read)
  ser.PortName = "COM1"
  ser.BaudRate = 2400
  ser.Parity = Parity.None
  ser.StopBits = StopBits.One
  ser.Handshake = Handshake.None
  ser.ReadTimeout = 500
  ser.WriteTimeout = 500
  ser.Open()
  cont = True
  readThread.Start()
  While (cont)
   message = Console.ReadLine()
   If message = "p" Then
    cont = False
   End If
   ser.WriteLine(message)
  End While
  readThread.Join()
  ser.Close()
 End Sub

 Public Shared Sub Read()
  While (cont)
   Try
    Dim charAsInt As Integer
    charAsInt = ser.ReadChar()
    Dim message As Char = Chr(charAsInt)
    Console.WriteLine(message)
   Catch ex As Exception
    'Do nothing
   End Try
  End While
 End Sub

End Class

As you can see it allows you to type whole strings to a console and send them.  Data is received 1 character at a time.